In addition to my K&N Typhoon Cold Air Intake

l have a friend who has a magnaflow on his 07 and it sounds pretty good and has a lifetime warranty. Is in the moderate price range but the warranty is nice l have had a magnaflow on my car for 5 years now and still looks new havent had to use the warranty yet.

http://magnaflow.com/04sound/04sport.asp

Scroll down the page and you can actually hear sound clips of the exhaust kit for your car. It says 04-06 but it fits 07 as well.

l have a Magnaflow Cat back Exhaust, that has been installed for the last 3 years. l like it. However, l think the Borla Cat back Exhaust sounds better on the Mazda3. Borla may cost more than Magnaflow, this l am not sure, however, with either u will be pleased. The K&N CA l & a Catback Exhaust is a wonderful thing. l have said this repeatedly, plan to purchase Dynamat or Hushmat & place it in the rear trunk space, including the location of the spare wheel. The same with the rear wheel well, including the front door panels, if u can swing it. The Cat-back exhaust will increase the noise level in the car, but if u add one of the aforementioned insulation products, it will improve the acoustics of ur stereo, reduce the drone in the cabin of the sedan that comes with this modification, & for u it reinforces the refinement of the vehicle. It takes away that ''economy'' feel & sound on the road, when more robust improvements r made. The performance is not as noticeable in 1rst & 2nd gear, in 3rd the CA l & Cat-back r coming on line. You will love it on open throttle from 80 to 118mph. Remember that the CA l in cold weather may cause the fuel to run a little rich, u may hear a burble & an occasional backfire because the heat generated in the combustion system is reduced due to the volume of cold air which does not always allow the complete atomization of the fuel burned. The Mass Air Flow meter should adjust once it is accustomed to the additional air in the system. The current set up is air starved, in comparison. Enjoy.